Molding of extruded materials to form countless products is widely done. As is well known, an extruder is used to provide the extruded material to a suitable die in which the extruded material is shaped to create the desired object. Commonly, the object which is created has a uniform continuous shape, such as conduits, pipes and flat sheets.
Extruded sheets, for example, may be formed from many different materials, with many different thicknesses, and with different layer constructions. An extruded sheet may be formed by itself or combined with one or more other sheet layers that are concurrently formed, or combined after formation. In a typical apparatus for extrusion forming of sheet products, a roll stand is placed downstream of an extruder assembly with an associated sheet die. Flowable material is delivered from one or more extruders through the sheet die to a nip/lamination location between adjacent rolls on the roll stand.
Apparatuses for forming an extruded sheet products are shown, for example, in my U.S. Ser. No. 12/455,353, entitled “Height Positioning Mechanism for Roll Stand Assembly on an Apparatus for Continuously Forming an Extruded Sheet Product”, filed Jun. 1, 2009; U.S. Ser. No. 12/455,344, entitled “Linear Bearing Assembly to Guide Movement of Roll Stand on Apparatus for Forming an Extruded Sheet Product”, filed Jun. 1, 2009; U.S. Ser. No. 12/455,376, entitled “Gap Adjusting Mechanism for Rolls on a Roll Stand Used in the Extrusion Forming of a Sheet Product”, filed Jun. 1, 2009; and U.S. Published Patent Application No. US-2010-0038037-A1, entitled “Apparatus for Applying a Film to a Bottom Side of an Extruded Sheet”, published Feb. 18, 2010. The disclosures of all of these patent applications is hereby fully incorporated by reference.
Moreover, various products, including sheet products, can require the use of two separate materials, such as shown, for example, in U.S. Publ. Application No. US-2008-0314525-A1, entitled “Web Lamination System”, published Dec. 25, 2008, the disclosure of which is hereby fully incorporated by reference. Molding of such products requires the supply of material from at least a first extruder assembly and a second extruder assembly, with a first material provided by one and a second material provided by the other. It should be appreciated that use two different materials may from time to time be switched. For example, when the two materials differ in color, or in texture, it may be desirable to form a product (e.g., a sheet material) having one color or texture on its outer skin, and also to form a similar product but with the other color or texture on its outer skin. This may be accomplished by swapping the connection between the outputs of the extruder assemblies to the inputs of the mold.
It should be appreciated, however, that swapping connections can result in bleed over and mixing of materials in the lines between the extruder assemblies and the mold. If, for example, one of the materials is hidden on the interior of a sheet, covered by the other material on the skin of the sheet, such mixing of materials in the unseen interior of the sheet may not be a major concern. However, similar mixing of the material which is molded to form the skin of the sheet can cause the sheet to have a different visible color than desired, either through some mixing of the colors or a speckling of one color with the other. Such an appearance is not only not what is desired, but it can give the appearance that the sheet was poorly manufactured, and possibly make the sheet unacceptable to a buyer.
The present invention is directed toward overcoming one or more of the problems set forth above.